Vehicle with a resiliently suspended cab part, particularly a driver&#39;s cab

ABSTRACT

A vehicle comprising a frame and a cab or the like supported by the frame by a resilient suspension, the resilient suspension is essentially constituted by a main U-shaped torque rod interposed in slanting or horizontal position between the frame and the cab, a main actuator being associated to the said main torque rod to determine its neutral position.

FIELD OF THE INVENTION

The present invention concerns improvements made to the resilientsuspension of the cab or cab part, and particularly the driver's cab, ofvehicles, in particular land vehicles.

BACKGROUND OF THE INVENTION

This type of suspension applies most particularly to the suspension ofcabs of all-terrain vehicles such as works vehicles (public works, farmwork especially to farm tractors, forestry work, mines, etc.), but alsoto the suspension of lorry cabs, and could have applications in otherfields.

It is known, for example in respect of farm tractors or lorries, for thedriver's cab to be disconnected from the frame and for suspension meansto be interposed and placed at the four corners of the cab with either apassive structure (springs, shock mounts), or an active for examplepneumatic structure (for example FR 2 661 387). However, this type ofsuspension only acts vertically and does not offset the transversemotions to which the cab is subjected.

Crossbars have also been connected to the previous components in anattempt to stabilise the cab (see for example FR 2 675 456, FR 2 653733, FR 2 607 459): but this solution, although managing to improve thevertical suspension, has not had a satisfactory outcome in terms ofdamping transverse motions of the cab.

The use of torque rods can certainly allow cab stabilisation to beimproved, but the result is an increase in the number of connectionsbetween the frame and the cab: vibrations of the frame are then easilytransmitted to the cab and the noise level in the latter is relativelyhigh. The document DE.A.30 00 606 shows such an arrangement with torquerods.

Lastly, stabilising devices use numerous active driving components whichconsiderably increase the cost of the installation and do not encouragethe idea of their introduction as standard to vehicles which are not topof the range vehicles.

SUMMARY OF THE INVENTION

The object of the invention is thus essentially to overcome thedrawbacks and shortcomings disclosed by the prior art, and to offer animproved technical solution for the effective suspension andstabilisation of a vehicle cab relative to the frame, which uses a smallnumber of parts connecting the frame and the cab so as to reduce thetransmission of noise in the latter, which uses a very small number ofactive actuators so as to reduce the cost of the installation, and whichto very great advantage uses combinable but distinct subassemblies toprovide the various types of compensation (vertical suspension, pitchingcompensation, rolling compensation, front-rear shock absorption) so asto constitute a modular structure enabling user requirements to be metexactly.

All things considered, the invention aims to offer an improved solutionwhich is more effective and less expensive than currently knownsolutions, and the modular structure of which admits of multiple uses.

To these ends, a vehicle comprising a frame and a cab or cab part or thelike supported by said frame by resilient suspension means ischaracterised essentially, being arranged according to the invention, inthat the resilient suspension means are essentially constituted by amain U-shaped rod interposed in an inclined or horizontal positionbetween the frame and the cab, a main actuator being connected to saidmain U-shaped rod to determine its neutral position. Said main actuatormay be a passive actuator (spring, possibly connected to a shockabsorber for example) or else an active actuator (for example ahydraulic or air jack possibly connected to a shock absorber).

Certainly, it is already known for at least one U-shaped rod to beinterposed between a frame and a cab part, for example, a driver's cab,resiliently suspended on the latter, as shown for example in the alreadymentioned document FR 2 607 459. However, such a U-shaped rod functionsexclusively as an anti-roll rod and in no way functions as the mainresilient suspension feature of the cab on the frame, the mainsuspension function being allocated to a set of components (springs andshock absorbers) placed at the corners of the cab according to aconventional configuration set out above and with the aforementionedassociated drawbacks.

The fact of providing the main suspension with a single solitaryU-shaped rod considerably restricts the connections between the frameand the suspended cab: the rod is fixed by one (or two) mounting(s) atits base and by two rotating articulations at the ends of its armsrespectively. Sound bridges between cab and frame are thus reduced, and,when the cab part thus suspended is the vehicle driver's cab, thesoundproofing of the latter can be very markedly improved, and at lesscost, compared with current practice.

In addition, the U-shaped rod constituting the sole main suspensioncomponent, the cost of the cab suspension is markedly reduced.

Lastly, as will become clear later, it is possible to connect to thissimple elementary main suspension other components appropriate forproviding additional functions. It is thus possible to constitute amodular system allowing different levels of technical equipment andprice which is able, from a minimum structure constituted by theU-shaped rod main suspension, to equip various ranges of vehicle:adaptation can be made on demand as a function of the technical andeconomic requirements to be met and the result is a marked reduction inthe cost of each individual piece of equipment whatever its level ofefficiency.

In a practical version which seems bound to be generally favoured, theU-shaped base formed by the main rod is fixed to the frame and the freeends of the arms of said U are fixed to the cab.

As regards the placing of the main suspension rod, it may beanticipated, also as a general rule, that the arms of the main U-shapedrod extend parallel to the vehicle longitudinal axis and are locatedapproximately symmetrically relative to said axis; equally well then, asa function of the general configuration of the vehicle and the availablespace between the frame and the suspended cab, the base of the mainU-shaped rod may be located approximately under the rear of thesuspended cab, with the two arms pointing forwards, or else the base ofthe main U-shaped rod may be located approximately under the front ofthe suspended cab, with the two arms pointing backwards. But it wouldalso be conceivable for the main rod to be placed transversely to theframe.

It is highly desirable to ensure that to the resilient suspension meansare additionally connected cab pitching motion control means, whichmeans may be designed in any ways suitable to meet the objective sought.However, in order to retain a simple and inexpensive structure and inorder to ensure structural independence with the main suspension meansso as to retain a modular aspect to the equipment, use may, preferably,be made for example of one of the following arrangements: pitchingmotion control means include a secondary U-shaped rod interposed betweenthe frame and the cab, this secondary rod determining at least a thirdsupport point of the cab not aligned with the two support pointsdetermined by the main rod; or else include at least one rod or strutparallel to the arms of the main U-shaped rod connected witharticulations to the cab and to the frame, said rod extending outsidethe plane defined by the main U-shaped rod in such a way that adeformable parallelogram layout is formed and interposed between the caband the frame; or else again include at least two superposed crossbelts, integral with the frame, determining a race for two rollers,separated longitudinally from each other and supported by the cab.

It is also possible to ensure that to the resilient suspension means areadditionally connected cab rolling motion control and transverseattitude correction means, the main U-shaped rod being constituted bytwo half-rods the respective arms of which are angularly independent ofeach other and between which are interposed said rolling movementcontrol means.

Then it is possible to use one of the following particular arrangementsin which the rolling motion control means include:

shock absorption means interposed between one of the arms and a strutwhich is integral with the other arm being located close by and above orbelow the aforesaid first mentioned arm;

an oscillating crossbar which is supported centrally and which joinstogether the two arms of the main U-shaped rod, second actuator meansbeing connected to said crossbar to bring about its controlledoscillation;

shock absorption means in a deformable rhombus determined by one of saidarms, an auxiliary arm integral with the other arm and two rodsarticulated on these and articulated to each other with bi-directionalresilient retraction.

contra-rotating rotating components appropriate for converting thedisplacement travel of one of the arms in one direction intodisplacement travel in the opposite direction and of the same amplitudeof the other arm.

To advantage, it is possible to ensure that to the resilient suspensionmeans are additionally connected front-rear shock absorption means whichare interposed between the frame and the suspension means of the cab sothat, particularly when the suspended cab is the vehicle driver's cab,the cab occupants and particularly the driver do not experience theviolent jolts caused for example by a trailer coupled to the vehicle.These front-rear shock absorption means may, in a simple way, include asub-frame oscillating mounted freely rotating on the frame andsupporting the main U-shaped rod, resilient components being placed oneither side of said support following the longitudinal direction of thevehicle so as to provide bi-directional longitudinal shock absorption.

It thus becomes clear, as had been suggested above, that the variousfunctions of suspension and shock absorption are provided bystructurally distinct, but combinable, means which allow every mutualcombination around the base structure of the main suspension withU-shaped rod, depending on the type of equipment required for vehiclesaccording to their anticipated uses and/or the degree of comfortrequired.

It also becomes clear that the main intended application for the use ofthe invention lies in the suspension of a vehicle driver's cab,particularly for a land vehicle, and particularly an all-terrainvehicle, and more particularly still (although not exclusively) a farmtractor.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood by reading the followingdetailed description of some versions given as absolutelynon-restrictive examples. In this description, reference is made to theappended drawings in which:

FIGS. 1 and 2 show diagrammatically, in perspective, two preferredversions respectively of a vehicle cab main suspension arrangedaccording to the invention;

FIGS. 3 and 4 show, in side diagrammatic view, two versions respectivelyof cab pitching motion control means in association with main suspensionmeans according to FIGS. 1 and 2;

FIGS. 5 to 13 show diagrammatically, either in perspective or from theside, different versions of cab rolling motion control and rollcompensation means in association with the main suspension means inFIGS. 1 and 2, and possibly in combination with pitching control means;and

FIG. 14 shows diagrammatically, in perspective, a preferred version offront-rear shock absorption means to which the cab is subjected.

DETAILED DESCRIPTION OF THE INVENTION

In the whole set of drawings the outline of the main features of avehicle are shown diagrammatically in a dotted lines, whereas thecomponents specific to the invention are drawn in ordinary lines. Thevehicle drawn as an example is a farm tractor with a suspended driver'scab, it being understood that the specifications of the invention canequally well be applied to numerous other types of vehicles.

Referring firstly to FIG. 1, a vehicle such as a farm tractor comprisesa frame 1 supported by a rear wheel axle unit 2 and a front wheel axleunit 3. Approximately the front half of the vehicle superstructure isoccupied by drive means housed under a front bonnet 4 resting on theframe 1. Approximately the rear half of the vehicle superstructure isoccupied by a driver's cab 5, located to the rear of the engine bonnet4, and resting on the frame 1 by resilient suspension means 6.

As can be seen perfectly in FIG. 1, the resilient suspension means 6essentially consist of a main generally U-shaped rod 7 interposed inapproximately inclined or horizontal position between the frame 1 andthe driver's cab 5, an actuator being connected to the U-shaped rod todetermine its neutral position. In FIG. 1, the actuator is supposed tobe of the passive type and constituted by a spring 8 housed in theU-shaped rod mounting 7.

In the example shown in FIG. 1, the U-shaped rod 7 is fixed, by its base9 (or bottom of the U) to the frame 1, whereas the respective free endsof its arms 10 a and 10 b are articulated to rotate freely on the lowerface of the cab 5 floor. For example, the articulation of the ends ofthe arms 10 a and 10 b is carried out on two respective spindles 11integral with two plates 12 fixed to the cab floor.

The base 9 of the U extends transversely to the vehicle longitudinalaxis and approximately symmetrically relative to said axis. Said base 9of the U is here located towards the rear of the frame whereas the twoarms 10 a and 10 b extend towards the front of the vehicle. Clearly, areverse arrangement could equally well be adopted, the base of the Ubeing located towards the middle of the frame 1 and the two arms 10 aand 10 b extending towards the rear of the vehicle as shown in FIG. 10.

Likewise, the U-shaped rod 7 could be arranged in an upturned position,its base 9 being located at the top and fixed under the cab floor andthe two arms 10 a and 10 b being inclined or horizontal downwards,forwards or backwards according to the arrangement selected, with theirends articulated to rotate on the frame.

In FIG. 2 is shown a version variant of U-shaped rod suspension whichuses an active actuator. This actuator may be of any professionallyknown type which is appropriate to ensure the required rod 7 retractionfunction. In this example, the active actuator includes a pneumaticspring 14 powered from a compressor (not shown) by means of anelectrically operated valve 15; the pneumatic spring 14 is interposedbetween one of the rod 7 arms 10 b and the frame or a support part suchas a coupling plate 16 integral with the frame. A shock absorber 17 maybe preferably placed in parallel on the spring 14 or combined with it.Preferably, to the pneumatic spring 14 are connected control meansarranged so as to modify, either continuously, or discontinuously, theshock absorption curve of this pneumatic spring (dynamic control). Inthe assembly in FIG. 12, the plates 12 fixed under the cab are in theform of clamps and the ends of the arms 10 a and 10 b of the main rod 7are directly connected to them with articulation.

It will be noted that the pneumatic spring additionally enables theneutral position level of the arm 10 b, and therefore the height of thecab relative to the frame, to be adjusted.

The suspension 6 which has just been described is certainly appropriateto fulfil the essential function of resilient suspension of the cab 5vis-à-vis the frame 1 and in this respect it represents the basestructure which must be interposed between the cab and the frame.However, this suspension is not able, by itself, to fulfil auxiliaryfunctions intended to improve cab stability, such as compensation forpitching motions, compensation for rolling motions and attitudecorrection, front-rear shock absorption, etc. It is then necessary toattach to the suspension 6 one or more auxiliary structures.

Furthermore, the suspension arrangement according to the inventionprovides only two support points for the cab and at least a thirdsupport point, or even additionally a fourth support point, must beprovided furthermore so that the cab is supported in a stable way.

The flexibility of the suspension 6 is expressed by a front-rearvertical oscillation motion (pitching motion) of the cab which, fordriver comfort and vehicle driving safety, it is very desirable tocontrol.

Provision is therefore made, in this context, to attach to the mainU-shaped rod 7, in a way functionally independent of the latter, caboscillation or pitching motion control means 18 which, to advantage, canadditionally be structurally arranged so as to constitute the aforesaidthird (or even the aforesaid third and fourth) cab support point. Thepitching motion control means 18 may make use of various technologicalsolutions, among which can be counted, as examples, the following.

In FIG. 3 in which the tractor is partially shown diagrammatically inside view, the resilient suspension 6 is of the type shown in FIG. 1.The pitching motion control means 18 include, on each side of the cab,two idlers 19 fixed to front and rear of the cab, under the latter. Forits part the frame supports, on each side, two flexible connections 20(cable made of stranded wire or synthetic material), superposed andcrossed, between which are engaged the two rollers 19 in such a way thatthe two flexible connections 20 are conformed in two horizontal andintersecting Z shapes.

The flexible connections 20 thus constitute a race for the rollers 19such that the cab is uncoupled from the frame 1 for all verticaloscillation motions induced by the suspension 6.

Another version of the pitching motion control means is shown in FIG. 1.The means 18 ₂ include a secondary U-shaped rod denoted as 21 which isinterposed between the cab and the frame. This U-shaped rod 21 may beplaced so that its base 22 fixed to the frame extends parallel to thevehicle axis and so that its arms 23 extend transverse to said axis; atthe ends of the arms 23 are articulated rods 24 connected, at their end,with articulation to the cab 5 floor. The two rods 24 may have differentlengths if the cab 5 floor is not parallel to the frame as shown inFIGS. 6 and 7. Clearly, the U-shaped rod 21 could also be placed withits base 22 extending transverse to the frame as shown in FIG. 10.

Yet another version of the pitching motion control means, denoted as 18₃, is shown in FIG. 4 in which the tractor is shown, partially, in sideview. The articulations 12 of the arms 10 on the cab are here such thatsaid arms form two inclined struts. By way of example, for the rest theactive actuator suspension has been shown in FIG. 2, including apneumatic spring 14. The pitching motion control means 18 include atleast one additional arm or strut 13 parallel to the arms 10 andarticulated at its ends on the frame and cab respectively in such a waythat the main rod 7 and the strut 13 constitute a deformableparallelogram capable of countering the relative pitching motion of thecab vis-à-vis the frame. There may be a single strut 13 placed in anyappropriate location, for example being located on the side and placedabove or below one of the arms 10 a and 10 b, or else being locatedbetween the arms 10 a and 10 b above or underneath the plane formed bythese so that the system forms a deformable parallelogram. Likewise, thepneumatic spring 14 may equally well be interposed between the frame andthe strut 13. It is also possible to provide two struts connectedrespectively to the two arms 10 a 10 b.

Furthermore, to the cab 5 resilient suspension means may be additionallyconnected to cab rolling motion control and transverse attitudecorrection means 25, said means solely being able to be connected to themain suspension means or else to be connected to the latter incombination with aforesaid pitching control means. A few versionexamples of this are given below.

As shown in FIG. 5, the rolling motion control and transverse attitudecorrection means 25 1 use a particular structure of the main rod 7,namely that the rod is constituted in two independent parts; a half-rod7 a is formed by a half-base 9 a and the corresponding arm 10 a, whereasthe other half-rod 7 b is disconnected from the previous one and isformed by a half-base 9 b (coaxial to the half-base 9 a and in itsextension) and the corresponding arm 10 b. As an example, an activeactuator formed by the pneumatic spring 14 and the shock absorber 17 hasbeen connected to the arm 10 b according to the diagram in FIG. 2.

The fixing of the two arms 10 a and 10 b is obtained by providingresilient means between the one and the other. In the version shown inFIG. 5, an auxiliary arm 26, integral with the base 9 a, extends closeto the arm 10 b and an actuator 27 is interposed between the auxiliaryarm 26 and the arm 27 so that the arm 10 a is uncoupled from the arm 10b.

The pneumatic actuator 14 and the shock absorber 17 provide the cabsuspension, as well as the cab height adjustment, as shown in FIG. 2,whereas the independence of the two arms 10 a, 10 b coupled up by theactuator 26 provides control of the transverse motion of the cab. Inorder to be certain of the functional independence of these twocontrols, it is desirable to use a rigid response actuator 26.

Clearly, the same functions may be obtained by using structuralarrangements which differ from the one in FIG. 5, which is shown only byway of example, in which the auxiliary arm 26 extends above the arm 10 band the pneumatic spring 14 is connected to the arm 10 b.

By way of clarifying concepts FIGS. 6 and 7 show two further examples ofthe same type. In FIG. 6, the auxiliary arm 26 extends under the arm 10b, whereas the pneumatic actuator 14 is interposed between saidauxiliary arm 26 and the frame. In FIG. 7, the auxiliary arm 26 alsoextends under the arm 10 b; but the pneumatic actuator 14 is transferredto the end of one of the arms 23 of the U-shaped rod 21 providingpitching motion control.

Another version 25 ₂ of the cab rolling motion control means consists inplacing the auxiliary arm 26, integral with one of the arms of thesuspension U-shaped rod, approximately parallel to the latter, incoupling it mechanically by a crossbar with the other arm (which isdisconnected from it), of the suspension U-shaped rod and in controllingthe oscillation of said crossbar in an approximately vertical plane soas to offset the cab rolling motion.

A first version example of the rolling motion compensation means 25 ₂ isshown in FIG. 8. Here, the auxiliary arm or strut 31 is integral withthe half-rod 7 b and extends, from the half-base 9 b, approximatelyparallel to the arm 10 b. The strut 31 and the other arm 10 a areconnected by a crossbar 32 which is susceptible to an oscillatingmotion, in an approximately vertical plane, around a median articulation33. Control of this oscillating motion may be obtained by means of anactuator 34 (for example a hydraulic or air jack) the rod of which beingapproximately parallel to the crossbar 32 is coupled to the latter by arigid connection 35. To advantage, the median articulation 33 of thecrossbar 32 is placed at the end of the pneumatic active actuator 14 rodwhich is responsible for the cab suspension and height adjustmentfunction.

FIG. 9 shows, in an end view, another version example of the rollingmotion compensation means 25 ₂ the composition of which is close to thatshown in FIG. 8. Here however the rod 36 of the pneumatic activeactuator is elongated so as to separate the crossbar 32 from theactuator 14 and the second actuator 37, such as an air or hydraulicjack, is placed at an angle between the foot of the rod 35 and theconnection point between the crossbar 32 and the arm 10 b.

Yet another version example of the means 25 ₂, with oscillating crossbar32, is shown in FIG. 10. Here the main U-shaped rod 7 providing the cabsuspension is placed contrary to the arrangements shown in the previousdiagrams, and the U-shaped rod 21 providing the pitching motion controlis placed longitudinally relative to the frame, and not transverse asshown in FIG. 1. One of the arms 23 of the U-shaped rod 21 remainsconnected to the cab floor by the rod 24 so as to constitute a third cabsupport point. But the other arm 23 of the rod 21 is connected with thepossibility of rotation to the aforementioned median articulation 33 ofthe crossbar 32 on the pneumatic actuator 14 rod. By means of thisarrangement, the actuator 14 provides the cab height adjustment byacting simultaneously on its three support points.

The rolling motion compensation means may also use, in another version,an arrangement 25 ₃ in a resiliently deformable rhombus interposedbetween the arms 10 a and 10 b.

A version example of such means 25 ₃ is shown in FIG. 11. An auxiliaryarm or strut 38 is integral with the arm 10 a at the opposite end of thehalf-base 9 a and is moved angularly (here downwards) relative to thearm 10 a so as to extend close to the arm 10 b and approximately underit. Two rods 39, articulated by one of their ends on the arm 10 b andthe strut 38 respectively, are articulated to each other by their otherend, in such a way that the arm 10 a, the strut 38 and the two rods 39form a deformable rhombus. A bi-directional retraction force towards areference position is provided by a pair of springs 40 mounted inopposition on the articulation of the rods 39. To ensure the correctoperation of the system, the articulation of the two rods 39 and thesprings 40 are enclosed in a tubular guide 41 which extendsapproximately along the bisector of the angle formed by the arm 10 b andthe strut 38, the two rods 39 being approximately of the same length.The pneumatic actuator 14 is, here, interposed between the frame(coupling plate 16) and the end of the guide 41 so that it can fulfilits dual function of main rod (7 a, 7 b) retraction and heightadjustment of the cab relative to the frame.

The rolling motion compensation means may also use, in another version,an arrangement 25 ₄ with contra-rotating rotating components coupledbetween the arms 10 a and 10 b.

A first version example of such means 25 ₄ is shown in FIG. 12. Thehalf-base 9 b connected to the arm 10 b comprises a shaft 42, coaxial tothe half-bases 9 a and 9 b, with which is integral a pinion 43 meshingwith a pinion 44 mounted fixed to a dummy shaft 45 parallel to the shaft42. To the half-base 9 a is connected an epicyclic train including ahollow internally toothed gear 46 integral with the half-base 9 a,coaxial to the shaft 42, with which meshes an internal gear 47 integralwith the shaft 45 to which it is coupled in translation, but not inrotation.

On the shaft 42 is loose mounted an arm 49 one end of which is connectedto the pneumatic actuator 14 supported by the frame and the other end ofwhich is mounted to rotate freely on the shaft 45. In the same way theshaft 45 is integral with the end of another arm 50 which extends closeto the arm 49 by being moved angularly relative to the latter and anactuator 51 is interposed between the other end of the arm 50 and thearm 49.

Any movement of one of the arms 10 a, 10 b causes, through means 42-51,an approximately identical movement and in the opposite direction of theother arm, so that the cab rolling motion is eliminated. The pneumaticactuator 14 retains its dual function of cab pitching motion and heightadjustment control relative to the frame.

FIG. 13 shows another version example of the means 25 ₄ in which thepairs of gears in the example in FIG. 12 are replaced by endless linktransmissions. To this end, the gears 43 and 44 are replaced by twowheels 52 and 53 wedged on the shafts 42 and 45 respectively andsupporting an endless link 54 with crossed strands so that the shafts 42and 45 rotate in opposite directions from each other. In the same waythe gears 46 and 47 are replaced by wheels 55 and 56 respectivelyintegral with the half-base 9 a and the shaft 48 respectively andsupporting an endless link 57 with parallel strands so that the twowheels 55 and 56 rotate in the same direction. The wheels and theendless links have to ensure rotation without creep and may be toothedwheels and chains or else pulleys and notched belts, particularly.

Lastly, it may be desirable to provide means suitable to absorb, at cablevel, the front-rear shocks to which the vehicle is subjected, such asfor example those transmitted by a trailer coupled to the vehicle. It isnecessary to this end for not only the cab, but also all the componentsof the means of suspension and control of its motions to be disconnectedfrom the frame with dual longitudinal resilient retraction forwards andbackwards respectively.

FIG. 14 shows a version of such means 58 which are here, as an example,connected to the suspension and rolling motion control means in FIG. 6,but which, clearly, could be connected to all the other types of meansgiven above.

The means 58 consist of a sub-frame which is interposed between theframe and the main U-shaped rod 7 of the cab main suspension 6. Thesub-frame 59 may for example consist of an approximately vertical framewhich is mounted (for example by one of its crossbars 60) rotating onthe vehicle frame 1 whereas its upper part (for example its uprights 61)supports freely articulated the half-bases 9 a, 9 b of the main U-shapedrod 7 of the main suspension 6. Two springs 62 are mounted at the frontand at the back respectively of the frame, with the possibility ofconnecting shock absorbers to them.

The sub-frame could also be arranged, for example in the form of acarriage connected to the frame with resilient retraction, so as tosupport additionally the pitching motion control means of the cab, withthe result that the latter would then be totally disconnected from theframe while retaining all the stabilising means envisaged in the contextof this invention.

Clearly, only a few version examples of the means provided according tothe invention have been more particularly described above and shown onthe appended drawings, and numerous other version forms could beenvisaged. However, these examples are sufficient to understand that thecab main suspension 6 may be achieved in a particularly straightforwardand cost-effective manner, while it may be implemented singly or incombination with additional means appropriate to fulfil optionalfunctions; said additional means may themselves be implemented singlywith the main suspension or connected, with each other, according tonumerous possible combinations, in combination with the main suspension.In this way a modular structure is constituted which is appropriate tofulfil a greater of lesser number of functions, according to the degreeof comfort and safety that it is wished to confer on the cab, and thatas a function of the price of the vehicle. It must also be pointed outthat the functions provided use a very small number of active actuators(one, or two at the most) which entails a very substantial reduction inthe cost of the whole suspension.

I claim:
 1. A work vehicle comprising a frame and a cab supported bysaid frame by resilient suspension means, wherein the resilientsuspension means include a main U-shaped rod interposed in inclined orhorizontal position between the frame and said cab, a main actuatorbeing connected to said main U-shaped rod to determine its neutralposition, wherein pitching motion control means of the suspended cab areconnected to said resilient suspension means and wherein said pitchingcontrol means include a secondary U-shaped rod, interposed between theframe and the cab, said secondary rod determining at least a third cabsupport point not aligned with said two support points determined by themain U-shaped rod.
 2. A work vehicle according to claim 1, wherein thepitching control means include at least one rod parallel to the arms ofthe main U-shaped rod and connected with articulations to the cab and tothe frame, said rod extending outside the plane determined by the mainU-shaped rod so that a deformable parallelogram layout is formed andinterposed between the cab and the frame.
 3. A work vehicle according toclaim 1, wherein the pitching control means include at least twosuperposed cross belts, integral with the frame, determining a race fortwo rollers, separated longitudinally from each other, supported by thecab.
 4. A work vehicle according to claim 1, wherein rolling motioncontrol and transverse attitude correction means are connected to theresilient suspension means, the main U-shaped rod being constituted bytwo half-rod the respective arms of which are angularly independent ofeach other and between which are interposed said means.
 5. A workvehicle according to claim 4, wherein the rolling motion control meansinclude shock absorption means interposed between one of the arms and astrut which is integral with the other arm being located close to andabove or below the aforesaid first mentioned arm.
 6. A work vehicleaccording to claim 4, wherein the rolling motion control means includean oscillating crossbar which is supported centrally and which joinstogether the two arms of the main U-shaped rod, second actuator meansbeing connected to said crossbar to bring about its controlledoscillation.
 7. A work vehicle according to claim 4, wherein the rollingmotion control means include shock absorption means in a deformablerhombus determined by one of said arms, an auxiliary arm integral withthe other arm and two rods articulated on these and joined to each otherwith articulation and dual resilient retraction.
 8. A work vehicleaccording to claim 4, wherein the rolling motion control means includecontra-rotating rotating components appropriate for converting thedisplacement travel of one of the arms in one direction intodisplacement travel in the opposite direction and of the same amplitudeof the other arm.
 9. A work vehicle according to claim 1, whereinfront-rear shock absorption means which are interposed between the frameand at least the cab suspension means are additionally connected to theresilient suspension means.
 10. A work vehicle according to claim 9,wherein the front-rear shock absorption means include a sub-frameoscillating mounted with free rotation on the frame and supporting themain U-shaped rod, resilient components being placed on either said ofsaid support according to the longitudinal direction of the vehicle inorder to provide bi-directional longitudinal shock absorption.
 11. Afarm tractor comprising a frame and a cab supported by said frame byresilient suspension means, wherein the resilient suspension meansinclude a main U-shaped rod interposed in inclined or horizontalposition between the frame and said cab, a main actuator being connectedto said main U-shaped rod to determine its neutral position, whereinpitching motion control means of the suspended cab are connected to saidresilient suspension means, and wherein said pitching control meansinclude a secondary U-shaped rod, interposed between the frame and thecab, said secondary rod determining at least a third cab support pointnot aligned with said two support points determined by the main U-shapedrod.